The invention relates generally to the reproduction of originals.
More particularly, the invention relates to a method and an apparatus for the reproduction of originals using electronic image processing.
In a known procedure for reproducing an original, the original is electrooptically scanned along rows and columns. The resulting imaging signals are electronically processed in an image processor to correct the same and the corrected imaging signals are then sent to a CRT (cathode-ray tube) printer. The latter prints an image of the original on photographic copy material.
Electronic image processing is being increasingly used in the reproduction of colored originals (positive-positive) and in the production of colored photographic positive images from colored negatives. See, for example, the European Patent Application Nos. 123,701 and 168,818. Basically electronic image processing is carried out by electrooptically scanning an original along rows and columns and correcting or modifying the resulting imaging signals in accordance with specific criteria. Scanning of the original is normally performed serially for the three primary colors red, green and blue (RGB). The modified imaging signals are sent to a color exposure unit designed to convert the electrical imaging signals into an optical image which is printed on photographic copy material, e.g., color positive paper. It is important here for conversion of the electrical imaging signals to be carried out such that the optical image is formed point-by-point. This makes it possible, in principle, for each image element or pixel to be subjected to image processing and to be subsequently printed on the copy material at a location corresponding to the coordinates of the image element or pixel on the original.
For a detailed description of the fundamentals of electronic image processing see, for instance, the following books: (i) F.M. Wahl, Digitale Bildverarbeitung, Springer Publishing House, Berlin, Heidelberg, N.Y., Tokyo (1984); and (ii) W.K. Pratt, Digital Image Processing, John Wiley & Sons, N.Y./Chichester/Brisbane/Toronto (1978).
In practice, economic considerations require color image reproduction systems to have high processing speeds. As a rule, the number of copies per hour exceeds 1000. Since an image is made up of approximately 1.5 million image elements or pixels and each pixel is commonly assigned a word length of 8 bits, there are 12 Mbits of data for each of the three color components red, green, blue. In total, then, 36 Mbits of data exist for a complete color image. It is clear that, which such a large quantity of data, the complicated operations which are carried out in the image processor to improve image quality have a marked influence on the processing time. The processing time for the entire color image reproduction system is determined by the following three basic operations: (a) scanning and reading in; (b) processing in the image processor; and (c) reproduction (color image printing). The time required for electronic image processing can be substantially reduced by employing a high-speed computer.